1. Field of the Invention
The present invention pertains to wire rope slings. More specifically, the present invention pertains to an improved circular wire rope sling or grommet and methods of making the same.
2. Description of the Prior Art
Wire rope consists of three basic components: (1) a core, (2) wires which form a strand and (3) multi-wire strands laid helically around the core. The wire can be made of any number of materials including steel, iron, stainless steel, monel and bronze. The most widely used material is high carbon steel. Strands are made up of two or more wires laid in any one of many specific geometric arrangements, or in combination of steel wires with some other material such as natural or synthetic fibers.
The core of wire rope is made of materials which will provide proper support for the strands helically laid therearound under normal bending and loading conditions. Core materials include fibers (hard vegetable or synthetic) or steel. A steel core may consist either of a strand or independent wire rope.
The construction of wire rope varies by the way wires are laid to form strands and by the way the strands are laid around the core. Strands are typically laid into the rope, to the right, in a fashion similar to the threading of a right hand bolt, i.e. xe2x80x9cright layxe2x80x9d rope. Conversely, xe2x80x9cleft layxe2x80x9d rope strands are laid in the opposite direction. Rope is also identified by the relationship of wires in the strands and may be identified as xe2x80x9cregular layxe2x80x9d, xe2x80x9clang layxe2x80x9d or xe2x80x9calternate layxe2x80x9d rope. The word xe2x80x9clayxe2x80x9d simply means the manner in which the wires in a strand or the strands in a rope are helically laid. The term xe2x80x9clay lengthxe2x80x9d is the distance measured parallel to the axis of the rope (or strand) in which a strand (or wire) makes one complete helical convolution about the core (or center).
Wire rope is frequently used to make slings for lifting heavy items. There are many types of slings which are identified by their particular construction or configuration. For example, there are single leg slings with sliding choker hooks, two leg bridal slings with sliding choker hooks, cable-laid slings with single rope legs, cable-laid slings with sliding choker hooks, multi-part braided slings and single leg slings with multi-part braided rope legs, etc.
A popular type of sling is the single circular or grommet sling in which a length of wire rope is cut, and the ends thereof joined in some manner to form a circle or loop. There are several styles of circular slings or grommets of the prior art which are identified by the way the ends are joined. In one style, the circular sling is totally strand laid and does not have any mechanical splices. In another style, wires of the rope are laid parallel at a splice point and held together by use of turn-back sleeves. This style of a sling does not have a splice at all and is subject to catastrophic failure when the sleeves fail. Another style sling requires the use of long splicing sleeves which hold the two ends together in a butt splice. Other circular slings or grommets have mechanically spliced joints which may require parallel strands and two splices at some point in the sling.
One of the problems in making and using slings of the prior art for large capacities is the increased length of the sling required by larger diameter wire rope. Thus, large capacity slings cannot be fabricated in the prior art in such a way as to allow for very low headroom conditions. Many times the headroom available for a large lift will not allow for the length needed. Therefore, such high capacity, low head room situations, have to be addressed with link plates, shackles or other specially engineered, costly and heavy solutions. Otherwise, the lift would have to be redesigned to allow for smaller lifts or longer slings. Longer slings permit greater movement of the load as the load gets further away from its attachment point and therefore lessen control of the load. Making numerous smaller lifts requires additional time, escalating the price of erection and/or removal of items being lifted. The same is true of the use of link plates or other specially engineered lifting devices.
The present invention provides a wire rope sling and method of making the same in which the rope is cut a predetermined length to provide first and second ends of the core and wire strands. In a preferred embodiment, the rope comprises six strands of wire helically laid around a core. Three of the strands are separated from the core and the other three strands, shifted or displaced along side the core and other strands a predetermined amount and rewoven with the core and other strands of wire into a continuous loop, the first and second ends of the three strands meeting along a continuous section of the core and other strands, the first and second ends of the core and other strands meeting along a continuous section of the three strands. A first splicing sleeve surrounds the first and second ends of the three strands and the continuous section of core and other strands and a second splicing sleeve surrounds the first and second ends of the core and other strands and continuous section of the three strands in a tightly gripping manner. The circular sling or grommet constructed in this manner provides a relatively low cost, low headroom sling with greater lifting capacity than any of the prior art. Utilizing working load limit charts, correct pins and connecting points can be determined without guess work. The unique design of the sling of the present invention results in a shorter sling of greater capacity and better load control. Many other objects and advantages of the invention will be apparent from reading the description which follows in conjunction with the accompanying drawings.